The present invention relates to a floor care machine, and more particularly, to a mobile, powered machine for curing a floor coating using ultraviolet (xe2x80x9cUVxe2x80x9d) light. The machine of the illustrated embodiment contemplates that a liquid floor coating be applied manually, but the invention relates, as well, to apparatus which both applies the liquid floor coating and cures it in situ.
U.S. Pat. No. 4,241,255 for ULTRAVIOLET RAY PROJECTOR discloses a machine for irradiating an applied floor coating with ultraviolet light to cure, and harden, the coating. This patented apparatus is particularly directed to manually manipulating the source of UV light to apply UV light to the coating in locations difficult to access, such as corners; and it discloses a manually-actuated shutter mechanism for controlling the application of the UV light to the coating being cured.
U.S. Pat. No. 4,999,216 for METHOD OF COATING CONCRETE FLOORS WITH PHOTOCURABLE COATINGS discloses a method of coating a concrete floor with a coating composition in liquid form and allowing the liquid to seep into the concrete surface to form a smooth coating, then exposing the coating to light in the ultraviolet and near visible range to cure the coating. Apparatus for carrying the source of ultraviolet light is disclosed only in schematic form.
As used herein, the terms xe2x80x9cfloor coatingxe2x80x9d or xe2x80x9ccoatingxe2x80x9d or xe2x80x9ccurable floor coatingxe2x80x9d and equivalents are intended to be broadly interpreted and refer to floor coatings applied in the liquid state and capable of curing to a solid state upon being irradiated by light. The light in the illustrated embodiment which effects curing is primarily in the ultraviolet region, but may include light in the near visible. However, the instant invention is not dependent on any particular coating materials. The invention relates to all materials which cure upon application of radiant energy (i.e., xe2x80x9cphotocurablexe2x80x9d materials), whether it is in the ultraviolet region primarily, or includes both ultraviolet, near visible and visible light, as persons skilled in the art of photocurable materials will understand. Such coatings are known, for example, as described in U.S. Pat. No. 4,999,216, and in copending U.S. provisional patent application for Ultra Violet Light Curable Floor Coating With Coloring Agent, filed Sep. 29, 1998 and bearing Serial No. 60/102,220. The radiant energy catalyzes a free radical polymerization and results in a fully cured coating in a matter of seconds, depending on the level of intensity of the radiated energy. An example of a curable floor coating requiring primarily ultraviolet light, has, as the two active elements, a urethane acrylate oligomer and an acrylated monomer blend. Curable coatings of this nature are commercially available and known in the art.
Thus, whereas the light source of the illustrated embodiment is primarily a source of ultraviolet energy, it is intended that the invention and the terms ultraviolet or xe2x80x9cUVxe2x80x9d include light sources of radiated photo energy of any wavelength or frequency which causes curing or cross linking or which catalyzes free radical polymerization of he applied photoreceptive materials to create the desired coating. The present invention does not contemplate limitation to any particular coating or to any band of photo energy other than that the material be capable of being cured from a liquid to a solid state upon exposure to photo radiation after the coating has been applied to a floor surface.
Sources of UV light in the form of fluorescent tubes have been developed for various applications. Some of these sources include a parabolic reflector to collect light from one side of the source and redirect it, focusing the light at a focal point (actually, a line parallel to the axis of the fluorescent tube and spaced from the axis at a known distance). Sources of UV light of this type for commercial use require substantial amounts of electrical power for operation. In order to achieve efficient and economical application of the light to a floor surface, for the present invention, it is desirable that the UV light source be maintained at a predetermined distance from the surface of application to maximize and control the application of UV power. Another known problem in using flourescent lamps is that the amount of radiant light energy produced by the lamp is a function of the temperature of the lamp, and it takes a substantial amount of time (in relation to the cure rate for available material) for the lamp to heat up to operating temperature for producing a constant or substantially constant level of irradiation (or power level). Using a lamp which has not achieved desired operating temperature could produce uneven results in curing, but initiating a start cycle after each lamp shut-off would result in appreciable delays.
Materials are known for producing a photocurable coating for surfaces, including floor surfaces, but applicants are not aware of any commercial machine currently available on the market for in situ application of photo energy to a curable coating. At least one of the reasons for which it is believed no commercial systems are currently available, is the problem associated with obtaining consistent results on the floor. The photocurable materials are cured at fast rates, but the cure rate or time is highly dependent upon the intensity of the light radiated on the coating. Cure is dependent on both the time of application and the flux density (i.e., intensity) of the light incident on the coating. The light flux density, in turn, is a function of the distance of the light source from the application surface, as mentioned above, and the power applied to the light, as well as the operating temperature of the light source.
Thus, consistent results cannot be obtained on the cured material unless the lamp has reached stable operating temperature. Likewise, results are inconsistent if the power to the lamp is changed, the rate of floor traverse of the machine is changed, or the height of the lamp is changed.
When all of these variables are considered, and particularly the fast cure rates of photocurable materials, it will be appreciated that commercial manufacturers of floor care machines have been reluctant to address the problems. It must be further appreciated that operators of floor care machines typically involve permanent maintenance personnel or contract maintenance personnel. Both such occupations are skilled in the mechanical manipulation of machinery such as buffers, burnishers, floor scrubbers and carpet cleaners, and have little or no experience in handling fast-curing materials curable upon exposure to photocuring light.
The present invention provides a mobile, motor-driven floor care machine which uses a programmable computer such as a microprocessor or other signal processor, data processor or controller for controlling the functions associated with ultraviolet curing of a floor coating by a driven (i.e., powered) machine. The machine has three basic modes of operations: Traverse (or Manual), Standby and Cure. These are sometimes referred to as the xe2x80x9csystemxe2x80x9d or xe2x80x9cmachinexe2x80x9d operating modes to distinguish them from the operating modes of the ballast which are independent operating modes. Briefly, in the Traverse (or xe2x80x9cManualxe2x80x9d) mode, the floor (or xe2x80x9ctraversexe2x80x9d) speed of the machine is under operator control. The Standby mode keeps the UV applicator powered at a level called a quiescent or steady state level, to greatly reduce the time to reach a Cure level. The traverse speed of the machine is also controlled by the operator in the Standby mode. In the Cure modes, the illustrated embodiment has three separate cure settings (Cure I, Cure II and Cure III), but the invention is not limited to the number of settings in a Cure mode of operation. For each Cure mode, the machine is driven at a predetermined speed, set by the microprocessor, and correlated with the power level of the UV lamp to achieve uniform dosage per unit area, and promote uniform cure results.
The illustrated machine is driven by an electric motor and includes driven rear wheels and a forward caster wheel for steering and mobility. A source of ultraviolet (UV) light or other source of curing radiant energy is mounted at the front of the machine near the floor. The UV light source is mounted in an enclosed housing provided with a shutter, and the housing is carried by a control or positioning linkage so that the light source may be raised for the Traverse mode, and lowered for the Standby and Cure modes. In the Cure modes when the machine is in motion, the shutter is open and the height of the UV light source is controlled by the processor to be within a predetermined height range above the floor.
In the Traverse mode, which is used to move the machine under power from one application site to another under operator speed control, the microprocessor: (i) turns off the ballast energizing the UV light source, (ii) closes the shutter of the UV applicator, and (iii) raises the housing for the UV light source to a transport position. In the Traverse mode, operation is manual, under the control of the operator, and a conventional motor drive system employing Pulse Width Modulation circuitry is used to energize a DC motor to power the machine. Speed may be varied by the operator, and the operator also has control over forward/reverse direction, using hand-actuated levers (or xe2x80x9cdirection actuatorsxe2x80x9d).
In the machine Standby mode, when selected by the operator, the UV lamp is energized to a quiescent state. This means that the UV applicator is at a level of electrical power lower than for curing operation but sufficient to reduce the time necessary to heat the lamp for Cure mode operation. In the quiescent state of the Standby mode, the UV lamp housing is lowered to the use or Cure position, and the shutter remains closed, but a cooling fan is turned on to cool the housing.
In each of the three Cure modes, a particular cure level is selected by the operator. The functioning of the machine is substantially the same for each Cure mode except that the traverse or floor speed of the machine for each Cure mode is predetermined and controlled by the processor, as a function of the cure rate selected by the operator. By way of example, Cure mode I may be of the highest power level or intensity of applied radiant energy, and thus be the fastest traverse speed. Cure mode II may have a medium intensity of applied radiant energy and a corresponding lower traverse speed. And Cure mode III is the lowest power level, and a correspondingly lower traverse speed. The total dosage of applied radiant curing light is substantially constant for each Cure mode, but the application time is different for each Cure mode.
In short, operation of the system in the three Cure modes is the same except that the intensity level of the ultraviolet light source is different, and the microprocessor sets a different traverse speed of the machine for each light intensity. The higher the intensity of ultraviolet light, the faster the machine will traverse the floor. Thus, in each of the Cure modes, the processor controls the ballast to energize the UV lamp at the desired power level. While the UV lamp is heating (a very short time compared to a complete start up from the off condition), the processor energizes an actuator which controls a linkage for positioning the UV lamp to the desired operating height. After a short time, of the order of a few seconds, the processor opens the shutter and actuates the traverse speed control to drive the machine, either in forward or reverse motion as selected by the operator, and at a speed set by the microprocessor depending upon the Cure mode selected by the operator.
Indicator lights are located on the control panel of the machine for indicating what mode has been selected by the operator and to display the status of operation.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment wherein identical reference numerals will refer to like parts in the various views.